Typical aircraft turbofan jet engines include an engine core, a nacelle that surrounds the engine core, and a fan that draws in a flow of air that is split into a bypass airflow and an engine core airflow. The nacelle provides a bypass duct that surrounds the engine core. The bypass airflow is transported through the bypass duct. The nacelle is configured to promote laminar flow of air through the bypass duct. The engine core includes a multi-stage compressor to compress the engine core airflow, a combustor to add thermal energy to the compressed engine core airflow, and a turbine section downstream of the combustor to produce mechanical power from the engine core airflow. The typical turbine section has two and sometimes three turbine stages. The turbine stages are used to drive the compressor and the fan. After exiting from the turbine section, the engine core airflow exits the nacelle through an exhaust nozzle at the aft end of the engine.
In a turbofan engine, the fan typically produces a majority of the thrust produced by the engine. The bypass airflow can be used to produce reverse thrust, typically employed during landing. A thrust reversing apparatus mounted in the nacelle selectively reverses the direction of the bypass airflow to generate reverse thrust. During normal engine operation, the bypass airflow may or may not be mixed with the engine core airflow exhaust prior to exiting the engine nacelle assembly. During thrust reverse operation, a translatable sleeve is moved from a stowed position to a deployed position to expose a cascade assembly, and blocker doors are deployed into the bypass duct. In this deployed position, the blocker doors redirect the airflow in the bypass duct to exit the nacelle out the cascade assembly.
A conventional cascade assembly provides reverse thrust operation, but may do so in an inefficient manner. Because of the momentum of the bypass airflow in the bypass duct, the majority of the reverse thrust is generated within the aft portion of the conventional cascade assembly. The forward portion of the cascade assembly has a “dead zone” in which relatively little of the bypass airflow is converted into reverse thrust. Thus, a majority of the bypass airflow is crowded into a relatively small area of the cascade assembly, which restricts the airflow exiting through the cascade assembly. The restricted airflow results in a reduced airflow exit velocity and, in turn, results in a reduced reverse thrust. These effects reduce the efficiency of the cascade assembly and of the engine. There is a need for an improved thrust reversing apparatus cascade assembly with improved efficiency.